Olfaction in vertebrates begins with the interaction of odor molecules with specific odorant receptors on sensory neurons. Each sensory neuron expresses only one or a few odorant receptors and therefore is functionally distinct. How is the specific identity of each sensory neuron determined? The experiments in this proposal address this issue by analyzing odorant receptor expression during sensory neuron regeneration in catfish. Through an analysis of the expression of odorant receptor genes at different stages of olfactory neuron differentiation, these experiments will allow us to address questions pertaining to when the functional specificity of a sensory neuron is determined and whether the olfactory bulb has any role in dictating receptor gene expression in olfactory sensory neurons.